According to ACOG Partogram guidelines and Zhang et al. (2010) re-evaluation of labour curves, which major revision to Friedman's classic labour curve is most clinically relevant for reducing unnecessary cesarean sections?

• A Active phase now begins at 6 cm cervical dilation, not 4 cm ✓
• B Normal latent phase is limited to 8 hours in nulliparas
• C Second stage limit is extended to 4 hours in nulliparas with regional anaesthesia
• D Deceleration phase has been recognised as a distinct fourth phase of labour

Explanation

Zhang et al. (2010, American Journal of Obstetrics and Gynecology) analysed contemporary labour data and found that the active phase of labour consistently begins at 6 cm cervical dilation in modern obstetric populations, rather than Friedman's 4 cm (1950s–60s data). This was incorporated into ACOG/SMFM Obstetric Care Consensus (2014) — the 'Safe Prevention of the Primary Cesarean Delivery' document — recommending that arrest of active phase be diagnosed only after ≥ 6 cm with ruptured membranes and ≥ 4 hours of adequate contractions (or ≥ 6 hours of inadequate contractions with oxytocin). This has significantly reduced the cesarean rate for 'failure to progress'.

Reference: Williams Obstetrics, 26th ed.

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Written and medically reviewed by the StethoPrep medical team.